Transformer help please

[rush2112]

I am installing a new 277/480 volt wye service in a facility. I wish to feed two other voltages from that service. The first being 120/208 wye and the second being 600 volt delta.

I wanted to order two transformers. The first one bieng 277/480 volt wye for the primary and 120/208 wye for the secondary. The suplly house is telling me this is a special transformer and it should be 277/480 volt delta X 120/208 wye. Can anyone help with this?

For the second transformer I was going to order a 277/480 volt wye X 600 Volt delta. Again the supply house says it should be delta to delta. I do not understand since my primary voltage is 277/480 volt wye. If anyone could help I would be very greatful.

 

[ron]

There is no real benefit from using the neutral on the primary side of the transformer. Select a delta primary and only bring 3 phases and the equip ground conductor to the primary. The neutral can remain unused at the service disconnect.

 

[iwire]

Welcome

Welcome

Welcome to the Forum Rush.

You have come to the right place there are members here that can tell you all you ever need to know about transformers.

You want a 480 Delta 208Y/120 and a 480 delta 600 delta transformer.

The fact you have a 480Y/277 service does not matter, you do not need the neutral on the primary sides of these transformers.

Do not take this wrong but have you wired this type of equipment and do you know the code requirements?

 

[hardworkingstiff]

I don't know as much about transformers as I should, but the Delta and Wye designations of the H side (I believe) refer to the way the transformer is wired internally. So feeding a Delta H side transformer from a Wye service is not a problem.

I've also read on this forum that a transformer with a Delta primary and Wye secondary will not pass harmonics from the L side to the H side. This is a very good thing.

 

[templdl]

This is the way that I would consided your application:
Delta/wyes are the logical choice in common applications.
As iwire stated just because you have a 480y/277, 3ph4w source doesn't mean that you have to have a wye primary of the same configuration.
Simply supply your new 480v delta pri. transformer's H1, H2, and H3 from the L1, L2 and L3 of the 480y/277 source and ignore the source neutral. However, bring the source EGC and bond it to the enclosure of the transformer.
When considering the 3ph 480v-600v step-up transformer you can go with the a delta-delta treating the primary in the same way. However, when considering the 3ph 600v secondary you must also think about the fact of if it is to be grounded are not. You may have a 600v ungrounded delta which I discourage unless there is a specific reason that you don't want to. If so, certain safety measures must be taken into consideration which may include a facility supervised by a qualified person as well as a means to detect a phase if it it goes to ground.
Otherwise consider a corner grounded delta.
In any event you must apply propery rated OCPDs remembering that you will have 600v to ground from the ungrounded conductors.
And don't overlook a 600y secondary. If you ground the X0 you will have 347v to ground which is much safer in the event of a ground fault.
Just a few thoughts that came to mind.
Dave T

 

[hmspe]

You want a 480 Delta 208Y/120 and a 480 delta 600 delta transformer.

I agree with the 480 delta to 208 wye, but not on the 480 delta to 600 delta. How do you establish an effective fault current path on a delta? It's been 20 years since I've dealt with this, but here's what I recall: Corner grounding works, but the maintenance staff will need to understand corner grounding, and it makes the other two phases run at 600V to ground. Adding a zig-zag transformer adds significant cost and instrumentation. It's a lot easier and cheaper to install 480 delta to 600 wye.

Like I said, it's been 20 years, so feel free to correct me if I'm missing something.

Martin

 

[iwire]

Corner grounding works, but the maintenance staff will need to understand corner grounding, and it makes the other two phases run at 600V to ground.

True enough.


However f it comes down to costs (and when doesn't it) I would expect corner grounded delta to be less expensive than a Wye system.

 

[LarryFine]

I tend to agree with Dave and Martin on using a Y secondary on the 600v system. The only difference would be grounding the neutral instead of a phase, and the neutral need run no farther than to its disconnect.

 

[iwire]

The only difference would be grounding the neutral instead of a phase,

And the cost of a delta Wye transformer over a delta delta (significant)

And the use of three pole equipment in place of two pole equipment, starters, breakers etc. (Assuming you can get what you need in two pole version.)

I believe you can sometimes use single phase panel boards with corner grounded delta.

I should say I have not worked on it myself.

 

[rush2112]

Wow.....I am shocked at the replies. You guys are great!!!! Thanks a million. Your input really helped me. The only thing I am not clear on is: the facility where I am working has an exsisting 600 volt delta service. I am adding an additional 480/ 277 Volt service to feed some new equipment. So I have the opertunity to refeed an exsisting 600 volt sub-service that is nearby the new service hence the 600 volt transformer question. I know if I put my wiggys from a 600 volt phase to ground it reads 277to ground but from phase to phase I read 600 volts. I asked the power co. what they were supplying and they said 600 Volt delta. So based on the earlier replies I see that I can use a delta for my 480 Volt primary side and a delta for my secondary side but what I am not sure of is the corner ground. I have never installed transformers before as I do a lot of control wiring. I just want to refeed the exsisting 600 volt equiptment from the new 480 volt service with out messing up the many motors that are on that old service.

And again you guys are great!! I hope I can help one of you with my knowledge one day.

 

[LarryFine]

The only thing I am not clear on is: the facility where I am working has an exsisting 600 volt delta service.

Can't you leave the 600v stuff on the existing service?

I am adding an additional 480/ 277 Volt service to feed some new equipment. So I have the opertunity to refeed an exsisting 600 volt sub-service that is nearby the new service hence the 600 volt transformer question.

Make sure there are no line-to-neutral loads if you go the Delta-to-Delta route on this one. (There probably aren't any.)

I know if I put my wiggys from a 600 volt phase to ground it reads 277to ground but from phase to phase I read 600 volts.

Now, that's weird! Did you check all phases? You should be getting either (1) the 347v mentioned by Dave (but not with Delta, unless there's a neutral-deriving means.), (2) 600v from two and 0 from one (corner-grounded Delta) or (3) almost nothing (ungrounded Delta, except for capacitive coupling to ground).

I asked the power co. what they were supplying and they said 600 Volt delta.

Again, must it go? Be sure to ask of a phase is grounded, and which one! I suggest studying the existing service very carefully before disconnecting anything.

So based on the earlier replies I see that I can use a delta for my 480 Volt primary side and a delta for my secondary side but what I am not sure of is the corner ground.

I can't go into too much detail, but simply put, one phase is grounded just like a neutral, including the coloring where accessible.

I have never installed transformers before as I do a lot of control wiring. I just want to refeed the exsisting 600 volt equiptment from the new 480 volt service with out messing up the many motors that are on that old service.

Don't forget that a transformer takes more current at 480v than it supplies at 600v. Please don't be offended, but this job sounds like it really needs the attention of an engineer or experienced master electrician.

And again you guys are great!! I hope I can help one of you with my knowledge one day.

You're welcome, be careful, and good luck.

 

[hardworkingstiff]

Please don't be offended, but this job sounds like it really needs the attention of an engineer or experienced master electrician.

I suggest you take Larry's advice. This job should easily afford an engineer's involvement, and that investment should keep you out of trouble.

 

[rush2112]

Larry, I called the factory today and changed my order. I ordered a 480 volt delta X 120/208 wye transformer and a 480 delta to 600 delta transformer. I went to work today with a multimeter and checked out my 600 volt cabinet. Here is what I found: Between A phase and ground.....285 volts, between B phase and ground.....390 volts, between C phase and ground...285 volts. Between all phases....610volts. All my voltages seem a little high. I did all my calculations for wire sizing, derating and over current protection and everything looks good.

 

[iwire]

Between A phase and ground.....285 volts, between B phase and ground.....390 volts, between C phase and ground...285 volts. Between all phases....610volts.

Rush that sounds to me like your dealing with an ungrounded 600 volt delta service.

A strange system if your not used to it.

Have you noticed any ground fault indicating lights?

Sometimes these are no more than six incandescent lamps arraigned in a "Y" pattern.

 

[rush2112]

Larry, I have not noticed any lights any where but I did call the factory and put th and e 600 Volt transformer on hold un til I find out whats going on here. I am not familier with 600 Volts but I have hooked up numerous motors in this facility And I just run my three conductors and my equipt ground and check rotation. The 600 volt service is very old and I see old labels calling it 500 volts, 550 volts, 575 volts and 600 volts. I am guessing its all the same. But I am not going to fool around with this until I have more info.....not to many people know about this 600 volts.

Also there is another 480 volt service in the plant and they are making 600 volts from that service too. ut they are using three small transformers that are 480 on the primary and 120 on the secondary. I am not really sure what they are doingwith this arrangement so I am going to wait and talk to some one who knows.

 

[LarryFine]

I went to work today with a multimeter and checked out my 600 volt cabinet. Here is what I found: Between A phase and ground.....285 volts, between B phase and ground.....390 volts, between C phase and ground...285 volts. Between all phases....610volts.

As Bob said, this sounds like a floating (ungrounded) system, which is okay. There are advantages and disadvantages to both grounded and ungrounded systems.

The reason you're getting any voltages at all to ground is because there is what's called "capacitive coupling" to the nearby earth and other large grounded surfaces.

If your meter were a greater load (i.e., less impedance), such as a solenoid-type tester, you'd likely read lower voltages.

 

[LarryFine]

Larry,

Bob, but who's counting?

I have not noticed any lights any where but I did call the factory and put th and e 600 Volt transformer on hold un til I find out whats going on here. I am not familier with 600 Volts but I have hooked up numerous motors in this facility And I just run my three conductors and my equipt ground and check rotation. The 600 volt service is very old and I see old labels calling it 500 volts, 550 volts, 575 volts and 600 volts. I am guessing its all the same. But I am not going to fool around with this until I have more info.....not to many people know about this 600 volts.

Good, cautious plan of action. I wish we could do more from a distance.

Also there is another 480 volt service in the plant and they are making 600 volts from that service too. ut they are using three small transformers that are 480 on the primary and 120 on the secondary. I am not really sure what they are doingwith this arrangement so I am going to wait and talk to some one who knows.

Sounds like they're using three individual transformers, which is perfectly acceptable; essentially a miniature version of what the POCO has on a pole-mounted 3-phase transformer bank.

My guess is that the three transformers are connected as 600v Delta to 208/120-Y. Can you see the connections and visualize the arrangement? Keep us apprised.

 

[jim dungar]

My guess is that the transformers are wired in a buck-boost delta arrangement to boost the voltage from 480 to 600V. I have done this often to run Canadian equipment in the US.

Many many years ago the nominal voltages were much lower than they are today. This had led to all sorts of weird voltages being reported, especially by us old timers that learned these old voltage levels.
For example, around the 40's the nominal motor voltages were closer to: 110, 220, 440, and 550.

The nominal supply (standard power transformers) voltages today are:120, 208, 240, 480, and 600.
These correspond to the nominal utilization equipment (motors) ratings of: 115, 200, 230, 460, and 575.

 

[rush2112]

You all sound like a bunch of good guys.....thanks a million!

 

[rush2112]

Well guys I got my service installed with my transformers and everything is working fine. Again thanks for the help. I do have another queation though. I am making 600 volts delta from my new 480 volt four wire service and the inspector brought up a point. He said that on the 600 volt service if a phase went to ground I would have no way of knowing it and it would not trip the breaker but it would still operate......for years even. But if another phase went to ground Then I would have a problem. So he recomended That I install pilot lights on each phase so if one leg went to ground a light would light indicating this. He also said a company makes this all wired up and I would just have to install it. However when I went to the suplly houses in my area no one new what I was talking about. I can make somthing with current transformers but I was wondering if any of you guys had any suggestions before I start constructing things.

Thanks.....RUSH